XkbKeyAction

NAME

SYNOPSIS

XkbAction XkbKeyAction(XkbDescPtr xkb,KeyCode keycode,int idx);

ARGUMENTS

- xkb

Xkb description of interest

- keycode

keycode of interest

- idx

index for group and shift level

DESCRIPTION

A key action defines the effect key presses and releases have on the internal
state of the server. For
example, the expected key action associated with pressing the Shift key is to
set the Shift modifier.
There is zero or one key action associated with each keysym bound to each key.

Just as the entire list of key symbols for the keyboard mapping is held in the
syms
field of the client map, the entire list of key actions for the keyboard mapping
is held in the
acts
array of the server map. The total size of
acts
is specified by
size_acts,
and the number of entries is specified by
num_acts.

The
key_acts
array, indexed by keycode, describes the actions associated with a key. The
key_acts
array has
min_key_code
unused entries at the start to allow direct indexing using a keycode. If a
key_acts
entry is zero, it means the key does not have any actions associated with it. If
an entry is not zero,
the entry represents an index into the
acts
field of the server map, much as the
offset
field of a KeySymMapRec structure is an index into the
syms
field of the client map.

The reason the
acts
field is a linear list of XkbActions is to reduce the memory consumption
associated with a keymap.
Because Xkb allows individual keys to have multiple shift levels and a different
number of groups per
key, a single two-dimensional array of KeySyms would potentially be very large
and sparse. Instead, Xkb
provides a small two-dimensional array of XkbActions for each key. To store all
of these individual
arrays, Xkb concatenates each array together in the
acts
field of the server map.

The key action structures consist only of fields of type char or unsigned char.
This is done to
optimize data transfer when the server sends bytes over the wire. If the fields
are anything but bytes,
the server has to sift through all of the actions and swap any nonbyte fields.
Because they consist of
nothing but bytes, it can just copy them out.

XkbKeyAction
returns the key action indexed by
idx
in the two-dimensional array of key actions associated with the key
corresponding to
keycode.idx
may be computed from the group and shift level of interest as follows: